Flame retardant for cellulosic fabrics

ABSTRACT

Flame retardants for cellulosic fabrics, especially polyester blends, comprise a limited phosphine oxide class of N-methylol propionamides, particularly N-methylol-3(dimethylphosphinyl)propionamide, closely related structurally to N-methylol-3-(dimethyl phosphono)propionamide, but markedly more effective as a flame retardant.

United States Patent 1191 Rivlin June 11, 1974 1 FLAME RETARDANT FORCELLULOSIC FABRICS [75] Inventor: Joseph Rivlin, Greensboro, N.C.

[73] Assignee: Burlington Industries, Inc.,

Greensboro, N.C.

[22] Filed: July 12, 1971 [21] Appl. No.: 161,867

[52] US. Cl. 8/ll5.7, 8/116 P, 8/184, 8/D1G. 4, 106/15 FP, 117/136,252/8.1,

260/56] R, 260/6065 P, 260/DIG. 24

[51] Int. Cl. D06m 13/28, D06m 15/54 [58] Field of Search 8/1 16.3, 116P, 115.7, 8/184; 106/15 FP; 252/8.1

[56] References Cited UNITED STATES PATENTS 2,691,567 10/1954 Kvalnes eta1 8/116 P 3,639,532 1/1972 Oerter et a1. 8/116 P 3,639,539 2/1972Nachbar et a1 8/116 P 3.766.252 10/1973 Schmidt et a1 252/8.I

OTHER PUBLICATIONS Anon., Textile World, p. 132, November, 1968.

Primary Examiner-George F. Lesmes Assistant Examiner-J. Cannon Attorney,Agent, or FirmCushman, Darby and Cushman [5 7] ABSTRACT 6 Claims, NoDrawings FLAME RETARDANT FOR CELLULOSIC FABRICS BACKGROUND OF THEINVENTION (dimethyl phosphono)-propionamide, 15,

O O (03:30)! CHgCHgPJNHCHgOH has achieved considerable commercialsuccess under the proprietary name of Pyrovatex CP. It is particularlyeffective because it bonds both phosphorus and nitrogen chemically tothe cellulose molecule. Being reactively bonded rather than merelyphysically coated onto the cellulose, it holds more tenaciously thannonreactive coatings and plasticizers. Besides this advantage PyrovatexCP, unless it is'combined with textile resins, has far less stiffeningeffect on fabrics than do the various kinds of coating agents.

Pyrovatex CP is not, however, without faults. As a phosphonate ester, ithas a potential for hydrolysis under conditions of extended use, asduring laundering, weathering, steam ironing, and the like. Moreimportant, the efficiency of the reaction between Pyrovatex CP andcellulose is low, thus resulting in considerable loss of expensivereagent during application to fabric. This low efficiency of reactionfurther manifests itself in the fact that only limited amounts ofPyrovatex CP can be added to cellulosic fibers, a fact which seriouslydiminishes its utility in fabric blends such as the popular 50/50polyester/cotton. Being inert to polyester and incapable of heavy add-onto cellulose, Pyrovatex CP cannot be taken up by the blends in amountssufficient to flameproof them adequately.

I SUMMARY OF THE INVENTION It is an object of this invention to providea class of flame retardants having a high capacity for bondingchemically with cellulosic fabrics. 1

A further object of the invention is to provide a class of flameretardants effective on polyester/cotton blends.

A further object isv to provide flame retardants with exceptionalresistance to laundering.

l havg found that new compounds, particularly where R, and R are methyl,ethyl, or porpyl radicals, and X is hydrogen or a methyl radical, areremarkably effective as flame-retardant reagents for cellulosic fabricsand fibers. The most preferredof these reagents is (CH ),P(O)CH,CHC(O)NHCH OH. Although obvi ously analogous to Pyrovatex CP in structure,it is surprisingly different from it in function and efficiency.

As shown hereinafter, the compounds of my invention exhibit high degreesand efficiencies of add-on to cellulosic fabrics and thereby confer ahigh level of flame resistance upon them. N-methylol-3-(dimethylphosphinyl)propionamide adds so well that it is effective evenon 50/50 polyester/cotton blend fabrics.

DETAILED DESCRIPTION This invention comprises a new class of phosphineoxide derivatives of N-methylol propionamides of the general formula R10 X 0 \II E g /BCH1 H NHCHzOR R:

where R represents hydrogen or alkyl of up to six carbon atoms, Xrepresents hydrogen or a methyl radical, and R, and R represent methyl,ethyl, or propyl radicals.

Preferred compounds are those having the formulas where R R and X are asdefined above. The most preferred compound isN-methylol-3-(dimethylphosphinyl )propionamide:

CH\3R O rornomii'miomon C IV These new compounds may be made by reactionof suitable Grignard reagents with dialkyl phosphites, the resultingdisubstituted phosphine oxides, also known as phosphinous acids, beingthereafter treated with acrylamide methacrylamide, and after that withformaldehyde, undergoing reactions comparable to those described in theaforementioned U. S. Pat. No. 3,374,292.

Two particularly surprising features distinguish the phosphine oxidecompounds of this invention from compounds known in the art: the highefficiency of their reaction with cellulose, and their superior flameretardant properties. Although neither of these advantages could havebeen anticipated, they are believed to work together to produce theremarkable overall superiority of these products. From a practicalstandpoint, the outcome of its particularly favorable combination ofproperties is that the preferred embodiment of this invention,N-methylol-3-(dimethylphosphinyl)propionamide, hereafter referred to forconvenience as MDMP, works effectively as a flame retardant even for50/50 polyester/cotton blends, an application where Pyrovatex CP fallsfar short of adequacy.

The aforementioned superior flame retardant capabilities of thesephosphine oxide compounds are believed to derive from several factors.The principal of these is the fact, taking MDMP versus Pyrovatex CP asan example, that MDMP has so much the greater capacity for bonding tocellulose. This capability is amply demonstrated in the examples. Afurther factor, perhaps less clearly marked in effect, is the fact thatthe mode of action of MDMP under the influence of flame seemsconsiderably different from that of Pyrovatex CP. This too is treatedfurther in the examples.

In addition to the foregoing unexpected advantages, these compounds,having no hydrolysis-susceptible phosphonate groups, and being membersof the class of phosphine oxides, among the most stable phosphoruscompounds known, are free from the potential of manyphosphorus-containing flame retardants, including Pyrovatex CP and itshomologs, for forming strong and deleterious phosphorus acid groups onexposure to laundering, ironing, weathering, and like hydrolyticinfluences.

At the same time, these compounds retain all of the advantages mentionedearlier for Pyrovatex: chemical rather than physical bonding tocellulose, simultaneous addition of both nitrogen and phosphorus in asingle reagent, and absence of stiffening and like defects commonlyassociated with flame-retardant coatings.

These compounds may be applied to substrates such as fabrics, yarns, andother forms of cellulose by any known means, such as spraying, dipping,padding, and the like, with preferably aqueous solutions of saidcompounds. The most convenient, and preferred, is padding, followed bydrying in the case of aqueous application. Application to the substrateis followed by a curing of cross-linking step, to effect chemicalreaction of the compounds hereof with free hydroxy groups in thesubstrate. This is preferably followed with a washing step to remove anyof the compounds not chemically bound to the substrate. Typically, thereaction or curing step is brought about by application of heat,although other suitable reaction or curing mechanisms may also beutilized. Heat is normally most convenient and therefore is presentlypreferred. The amount and duration of heat treatment will normallydepend on local practice, the type of substrate being treated, etc., andare not presently believed to be critical to the success of thisinvention. Usually a temperature of from about l50l75C for from aboutone to several minutes will suffice for the heating step.

It has not as yet been possible to provide reasons for the most trulyunexpected advantages of the products of this invention, theirremarkable efficiency or their extent of reaction with the fabricsubstrate. Considering the apparent similarity of the structures ofPyrovatex CP and these compounds, particularly MDMP, it would beexpected that Pyrovatex and MDMP would react with cellulosic materialsin essentially the same way. The structures differ by only the presenceof two extra oxygen atoms in Pyrovatex, and even these are at theopposite end of the molecule from the functional -CH OI-I group.However, the data given below show clearly that there is a remarkabledifference in reactivities, in favor of the compounds of this invention.

Not only are differences in reactivities apparent, but

even at comparable add-ons and phosphorus contents,

blend fabrics treated with MDMP are markedly more resistant to flamethan those treated with Pyrovatex CP. It is apparent that, despite theirclose structural resemblance to each other, MDMP and Pyrovatex CP areactually very dissimilar in effectiveness, and presumably in mechanismof flame-proofing action. These facts are particularly evident when onecompares their effects on 50/50 polyester/cottom blends.

It should be recognized that, while the primary emphasis herein is onfabrics of various types including percent cotton, 100 percent rayon,blends of such cellulosics with various man-made fibrous materials, andparticularly in blends with polyester, it is understood that thesstreatments are equally applicable to a broad variety of substrates whereflame retardancy may be desired, including yarns, fibers generally,paper, I

and other cellulose-containing materials, whether these be made fromcotton, rayon, wood pulp, or other sources of cellulose, and whether thearticles in which they are incorporated are intended for use in apparel,home furnishings, intermediate, or industrial type products.

In assessing the flame retardancy of both the compounds of thisinvention and of earlier known products, two methods of evaluation havebeen utilized. One is the vertical flame test, Fire Resistance ofTextile Fabrics," AATCC No. 34-1966. Greater reliance has been placed inthis specification on the measurement of the Limiting Oxygen Index, LOI,because it offers more potential for indicating the extent ofdifferences between test specimens, particularly those which fail, i.e.,burn entire length (BEL), in the vertical test and therefore cannot becompared in terms of char length. It has been found, in general, thatfabrics having LOI values above the range of about 0.240-0260 usuallypass the vertical test; i.e., they are selfextinguishing to the degreethat they do not burn their entire length, but instead have measurablechar lengths.

The LOI values recorded herein were measured on a slightly modifiedGeneral Electric Oxygen Index Flammability Gage, Cat. No. A4990A,following Instruction Manual 454 l KZS-OOIB. (See also ASTM Test D-2863,the standard LOI test used for plastics.) The application of the LOItest to fabrics is discussed in a paper by J. J. Willard and R. E.Wondra, Textile Research Journal, 40, 203-2l0 (1970).

Modiflcationslo the standard GE instrument (see ASTM Test D-2863 FIG. 1,for the meaning of the following apparatus terms) were as follows:inside diameter of glass cylinder 3 inches instead of 3% inches;distance from top of screen (4) to top of cylinder 11% inches instead of6 inches; distance from bead surface (6) to screen (4) 6% inches insteadof 3 inches; fabric length 6 inches instead of 5 inches; cover plateremoved.

Flow rate was set at 4 cm./sec.

Further details of this invention are given in the following examples.

EXAMPLE 1 As an illustration of the invention, N-methylol-3-(dimethylphosphinyl)propionamide, MDMP, was synthesized as follows:Dimethylphosphine oxide was prepared by the method of Hays, J. Org.Chem., 33, 3690 (1968), and distilled before use. To a stirred solutionof 271.7 g, 3.48 mol, dimethylphosphine oxide and 247.1 g, 3.48 mol,acrylamide in 319 ml ethanol was added dropwise a freshly preparedsolution of sodium ethoxide, made from 8.4 g, 0.365 atom, sodium and 193ml ethanol. After about one-fourth of the base had been added avigorously exothermic reaction began. When the reaction subsided theaddition was continued at a rate which maintained a temperature of7080C. The resulting white slurry was stirred 2 hours longer withoutheating, cooled, "filtered, and the solid 3-(dimethylphosphinyl)-propionamide separated and dried. The yield ofproduct melting l909lC was 483 Analysis:

Calcd. for C H NO P: C 40.2, H 8.05, N 9.39, P 20.8

% Found: C 39.9, H 7.84, N 9.36, P 21.7

A 95.1-g portion, 0.638 mol, of this intermediate was treated with 157g, 1.9 mol, of 36.6 percent formaldehyde solution at 60C. The pH washeld at 8-9 during the reaction by addition of a few small drops of 50NaOl-l. After 2.5 hours the free formaldehyde content, measured by thesodium sulfite method, was constant. After overnight stirring at roomtemperature, the solution was analyzed, it being found that the contentof N- methylol-3-(dimethylphosphinyl)-propionamide, MDMP, was 0.562moles in the 141 g of solution.

EXAMPLE 2 To illustrate the utility of the invention, in this andfollowing examples the procedure employed was to pad an aqueous solutionof reagent, 1 percent curing catalyst (2-amino-2-methylpropanolhydrochloride), and 0.1 percent detergent(nonylphenylpolyethyleneoxyethanol) onto weighed samples of bleached ornormally scoured, but otherwise untreated 100 percent cotton sheeting,50/50 polyester/cotton sheeting, or other eel; lulosic fabric in alaboratory padder at 30 psi; dry 4 minutes at 93C; cure 3 minutes at175C; process wash fi'minutes with water containing 0.001 percentdetergent in a home washing machine set on warm; tumble-dry; andcondition overnight at 72F and 65 percent relative humidity inpreparation for final weighing and testing. Except when otherwiseindicated, test fabrics were 100 percent cotton sheeting, 3.75 oz/yd, 95X 84 count, and 50/50 polyester/cotton sheeting, 3.68 oz/yd, 96 X 88count. Samples for treatment were usually about 10 X inches, weighingbefore treatment about 18 g for 50/50 polyester/cotton and 16 g for 100percent cotton. The treatment cycle was repeated more than one time whenever it was desired to increase the extent of modification (add-on)beyond the maximum obtainable in a single treatment. The most superiorresults were generally obtained when using freshly prepared paddingbaths.

EXAMPLE 3 For comparative purposes, samples of 50/50 polyester/cottonfabrics were padded with 40 percent aqueous solutions of Pyrovatex CPand MDMP by the procedure of Example 2. Though noneof the once-treatedsamples passed the vertical test, those padded with MDMP had slightlybut significantly higher L01 readings, as may be seen by comparison ofthe one-cycle entries in Tables 1 and 2. Two and even three cycles ofPyrovatex CP had almost no further effect on increasing the add-on andthe L01, and all specimens burned their entire lengths in the verticaltest. The L01 of the original fabric for all of the samples was 0.168.

TABLE 1 50/50 Polyester/Cotton Sheeting Padded with 40% Pyrovatex CP No.Phos- Vertical Padding phorus 7c Char Sample Cycles I 7! Add-on L01Length A 1 1.32 9.1 0.223 BEL B l 1.21 9.3 0.220 BEL C 2 10.7 0.231 BELD 2 11.0' 0.231 BEL E 3 1.72 12.5 0.231 BFL F 3 1.87 13.9 0.234 BELNote: *BEL=Burned Entire Length TABLE 2 50/50 Polyester/Cotton SheetingPadded with 40% MDMP No. Fhos- Vertical Padding phorus Char SampleCycles 7c Add-on L01 Length A l 1.44 9.6 0.229 BEL B 1 1.25 7.8 0.231BEL C 2 2.46 13.4 0.264 7.5" D 2 2.73 20.9 0.254 7.5" E 2 2.52 18.30.256 7.7" F 2 2.14 14.0 0.247 BEL G 2 2.19 1.50 0.251 3.8" H 2 2.6715.5 0.243 7.1" 1 2 2.52 15.0 0.236 8.1"

Surprisingly, when MDMP was applied the second time, the additionaladd-on was usually equal to and sometimes even greater than theoriginal, and the L01 readings were increasing materially. Mostsignificant of all, from a practical standpoint, was the fact that theL01 rose into the 0240-0260 range, and that the majority of the testspecimens no longer failed the vertical test. (A few did fail, but thiswas taken as verification of the known imprecision of the verticaltest.)

It is obvious, from the results in these tables, that MDMP displays aremarkably greater capability for bonding with and flameproofingpolyester/cotton blends.

EXAMPLE 4 To determine what range of polyester/cotton fabrics could beflameproofed with MDMP, samples of 65/35 polyester/cotton sheeting weretreated twice with 40 percent MDMP and Pyrovatex CP solutions by thestandard procedure of Example 2. Results are given in Table 3.

lts significantly higher L01 values showed that MDMP had effected asignificantly greater increase in flame resistance than did PyrovatexCP.

EXAMPLE For comparative purposes, the procedure of Example 4 wasrepeated, but this time by padding twice onto 65/35 rayon/polyestersheeting at 40 percent concentration according to the method of Example2. Two MDMP treated samples gave LO1 readings of 0.252 and 0.242. andboth samples passed the vertical flame test, giving char lengths of 6.3and 4.6 inches.

EXAMPLE 6 1n using relatively expensive flame retardants such asPyrovatex CP and MDMP, it is important to achieve a high degree ofbonding of the solution padded onto the fabric. Anything removed by theprocess wash after curing is essentially non-recoverable and wasted. Thedegree of bonding is expressed as the efficiency, this being calculatedfrom the equation:

Retardant retained after washing/Retardant padded on X 100 efficiencySamples of 100 percent cotton sheeting were put through one cycle of theprocess of Example 2, being padded with Pyrovatex CP and MDMP solutionsof different concentrations. Data obtained are shown in Table 4.

TABLE 4 Efficiency of Addition to 100% Cotton of Pyrovatex CP and MDMPat Different Concentrations From these results it is apparent that theefficiency of addition of M DMP approaches 100 percent at lowconcentration, while that of Pyrovatex CP peaks at around 55 percent.

Similar results, shown in Table 5, were obtained when solutions of arange of concentrations were padded onto /50 polyester/cotton sheetingin the same manner.

TABLE 5 Efficiency of Addition to 50/50 Polyester/Cotton of Pyrovatex CP and MDMP at Different Concentrations TABLE 5 4 Continued "/7; 7nRetardant Concn. Add-on P [5111- L01 ciency Do. 8.1 1.15 74 0.223 D0. 116.0 0.97 83 0216 Do. 6.3 0.91 92 0.218

These results show conclusively that MDMP. despite the similarity of itsstructure to that of Pyrovatex C P, possesses a radically differentdegree of affinity for cotton, this greater affinity making it capableof greater add-ons with less waste of reactant.

EXAMPLE 7 1t became apparent from L01 measurements of a large number oftest samples that at roughly equivalent phosphorus contents,MDMP-treated fabrics were proving statistically more resistant toburning than comparable Pyrovatex-treated fabrics. A series of bothgroups of fabrics were therefore submitted to burning in beakers in theLOl apparatus in oxygen concentrations at or above their LOl values. Thechars were weighed and analyzed, and the percentage of the originalphosphorus remaining in each char was calculated. Data are summarized inTables 6 and 7.

TABLE 6 Retention of Phosphorus in Char from Retention of Phosphorus inChar from MDMP-Treated Cotton and 50/50 Polyester/Cotton SheetingOriginal Samples '71 P in 71 P Retention L01 7: P Char by Char 100%Cotton 50/50 Polyester/Cotton From inspection of the last columns ofTables 6 and 7 it is immediately apparent that there is a very largedifference of kind in the retention of phosphorus by Pyrovatex-treatedversus MDMP-treated fabrics. Over twice as much Pyrovatex-addedphosphorus remains behind. This is interpreted as showing that the modeof flameproofing by MDMP is such that a far higher percentage of theagent operates in the vapor phase when the fabric is subjected toburning. Evidently this different and wholly unexpected mode of actionmakes each amount of MDMP somewhat more effective as a flame retardantthan a comparable amount of Pyrovatex CP.

Though it is not desired for this invention to be bound by the limits ofany mechanism, it appears probable that the phosphorus liberated intothe vapor phase above the burning fabric diminishes the flammability ofthe vapors, reducing their tendency to engulf the whole fabric in flame.This effect seems particularly advantageous where, as in the presentinvention, a significant portion of the retardant released by the cottonseems to be in a form more capable of affording maximum protection tothe polyester portion of the blend.

EXAMPLE 8 Samples of MDMP-modified cotton and 50/50 polyester/cottonsheeting were subjected to multiple washings in a home washing machineset on hot, in the presence of 0.l percent TIDE. home detergent. Thephosphorus analyses and LO! readings, before and after laundering, areshown in Table 8. It is evident that not only the phosphorus content butalso the flame resistance remained constant, within the errrors ofmeasurement of the methods.

1 claim:

1. A process for increasing the flame retardency of a cellulosic textilematerial which comprises impregnating the material with a solutioncontaining an acidic catalyst and a product of the formula:

where R represents hydrogen or alkyl of up to six carbon atoms, Xrepresents hydrogen or a methyl radical, and R and R represent methyl,ethyl or propyl radicals and thereafter curing the impregnated materialunder heating conditions.

2 Theprocess of clai rn l wherein tliecellulo sic tex tile material is a50/50 polyester/cellulose blended textile fabric, X is hydrogen and R ishydrogen.

3. The process of claim 1 where the c ellulosic textile material is apolyester/cellulose blended textile material.

4. T he process of claim 3 where i s hydrogen and X is hydrogen or amethyl radical.

5. The process of claim 3 where X is hydrogen.

ti The product produced by the product of claim 11 -w qTEIi STATESPATENT OFFICE (s/ss) CERTIFICATE OF CORRECTIUN Patent No. 3,816,068Dated. Juue 11, 1974 Inventor-(s) Joeeph Rivlin It is certified thaterror appears in the above-identified p atent and that said LettersPatent are hereby eorrected as shown below:

Column 1, line 61, "porpyl" should read -propyl- Column 2, lines 51-52,"acrylamide methacrylamide" should read --acry1amide or methacry1amideColumn 5, line 51, "when ever" should read -whenever Column 6, line 29,in the fourth column, l. 50"

should read --15.o--

Column 6, line 57, "CO" should read -CP- Column 9, line 25, "NDMP"should read --M DMP-'- Signed and sealed this 29th day of October 1974.-

(SEAL) Attest:

MCCOY M. GIBSON JR. c. MARSI IALL DANN Attesting Officer I commisslonerof Patents P -w I RTEo STATES PATENT- OFFICE CERTIFICATE OF CORRECTIONPatent No. 3,816,068 Dated June 11, 1974 Inventm-( Joseph Rivlin It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby eorrected as shown below:

Column 1, line 61, "porpyl" should read -propyl Column 2, lines 51-52,"acrylamide methacrylamide" should read -aerylamide or methacrylamideColumn 5, line 51, "when ever" should read whenever- Column 6, line 29,in the fourth column, "1. 50" v 2 should read -l5.0,- I

Column 6, line 57, "CO" should read --CP Column 9, line 25, "NDMP"should read -M.DMP-'- Signed and sealed this 29th dayof October 1974.-

(SEAL) Attest:

McCOY M. GIBSON JR. c. MARs ALL DANN Attesting Officer Commissloner ofPatents

2. The process of claim 1 wherein the cellulosic textile material is a50/50 Polyester/cellulose blended textile fabric, X is hydrogen and R ishydrogen.
 3. The process of claim 1 where the cellulosic textilematerial is a polyester/cellulose blended textile material.
 4. Theprocess of claim 3 where R is hydrogen and X is hydrogen or a methylradical.
 5. The process of claim 3 where X is hydrogen.
 6. The productproduced by the product of claim 1.